Increased levels of sex hormones in urine, often a result of obesity, warn of a heightened risk of breast cancer, according to a study published in the British Journal of Cancer.

The investigation, a collaboration between Dutch researchers and a leading Cancer Research UK scientist in Oxford, is the largest study to date on sex hormones in urine and their effect on breast cancer risk. It found that postmenopausal women with high amounts of certain types of estrogen and testosterone in their urine were at a greater risk of developing the disease.

Obesity is the biggest known reason for high levels of sex hormones among postmenopausal women. Cancer Research UK scientists believe that maintaining a healthy weight could help women bring down their breast cancer risk.

Earlier studies by Cancer Research UK have already established the link between increased levels of sex hormones in the blood and breast cancer.

In this study researchers measured the levels of two forms of estrogen and two forms of testosterone in urine samples from hundreds of postmenopausal women. For each of the hormones tested, scientists compared the women with the highest urine levels and those with normal levels.

They found that the group of women with the highest levels of one form of estrogen - called estrone - also had more than double the rate of breast cancer cases.

The group of women with the highest level of a type of testosterone had rates that were 70 percent higher than the women with normal levels.

Dr. Petra Peeters of the Utrecht University Medical Centre in Holland, says: "We know that reproductive and hormonal factors are involved in the development of breast cancer. This study confirms that high levels of sex hormones can raise risk."

Fellow researcher Dr. Tim Key of the Cancer Research UK Epidemiology unit at Oxford University, says: "This provides further evidence of the link between hormones and the risk of breast cancer."

Key explains that fat cells produce excess amounts of the hormone estrogen, which can speed up the natural process of cell division. The faster cells duplicate, the higher the chance that something can go wrong and that a cancer cell may form.

"In the future it might become possible to use the presence of sex hormones in urine to help monitor a woman's risk and to target screening at women who need it most," he adds.

SOURCES:
British Journal of Cancer, April 29, 2003
Cancer Research UK (http://www.cancerresearchuk.org)